The present invention relates to process variable transmitters. More specifically, the present invention relates to transmitters of the type which are used to control or monitor industrial processes.
Industrial processes are used in industrial manufacturing. There are various types of field devices which are used to monitor the process. For example, process variables such as pressure, flow, temperature and others can be sensed. In addition to using this information for monitoring the process, the process variables can be used to control the process.
Process variables are sensed using field devices known generally as process variable transmitters. In many instances, it is desirable to diagnose operation of the industrial process and identify the condition of the process and associated equipment. For example, diagnostics can be used to identify a failure in the industrial process, for example, so that failed components can be replaced. Other uses of diagnostics include identifying impending failure prior to its occurrence. This allows the component to be replaced or repaired at a desired time without necessarily shutting down the process.
Sensing vibrations is one method used for diagnosing process control devices. For example, a vibration sensor, such as an accelerometer, can be placed directly on a control device and can be used to sense vibration noise signals generated by the device. For example, the noise generated by a pump motor can be monitored. Vibrations are isolated and evaluated by identifying those which exceed an amplitude threshold or which have an abnormal frequency. This can be indicative of an actual or impending failure. Specific examples include sensors placed on a pump or a motor housing, discharge valves, or flanges associated with the control device. Another known diagnostic method is a manual inspection in which an operator listens for an abnormal sound from the control device. There is an ongoing need for improved diagnostic technology in industrial process control or monitoring systems for detecting failed components and components which have degraded or in the process of failing. Various techniques are shown in U.S. Pat. No. 6,601,005, filed Jul. 29, 2003 titled “Process Device Diagnostics Using Process Variable Sensor Signal; U.S. Publication No. 2005/0072239, published Apr. 7, 2005, titled “Process Device with Vibration Based Diagnostics” and U.S. Pat. No. 7,010,459, issued Mar. 7, 2006, titled “Process Device Diagnostics Using Process Variable Sensor Signal”.